<div id="demo">
    <h1>diff</h1>
    <p>{{foo}}</p>
</div>
<script src="http://unpkg.com/vue@3"></script>
<script>
    // 创建实例
    const app = Vue.createApp({
        data: () => ({ foo: 'foo' }),
        mounted() {
            setTimeout(() => {
                this.foo = 'fooooo'
            }, 1000);
        }
    }).mount('#demo')
</script>